;; minutes : Number -> Number;; how many minutes does it take Sis Y. Fuss to push a rock up a hill (30 up, 4 down);; (minutes 20) "should be" 1, because she reaches 30 and then doesn't slide back;; (minutes 30) "should be" 2, because she goes to 30, slides down to 26, and has to push again(define (minutes d) (ceiling (/ d (- 30 4))))